Electroacoustical apparatus



Oct. 31, 1939. .1. ANDERSON ELEQTROACOUSTICAL APPARATUS Filed June 30,1936 3 Sheets-Sheet 1 INVENTOR LfJL/f J? ANDEEJO/V Oct. 31, 1939. J.ANDERSON ELECTROACOUSTICAL APPARATUS Filed June 50, 1936 3 Sheets-Sheet2 INVENTOR $5 J 0E50N BY TTORN Y Oct. 31, 1939. L. J. ANDERSON 7 1ELECTROACOUSTICAL APPARATUS Filed June 30, 1936 3 Sheets-Sheet 3 i 2 mg5 fil INVENTOR LE5 J. N056 /V ATTORNEY Patented Oct. 31, 1939 UNITEDSTATES ELECTROACOUSTICAL APPARATUS Leslie J. Anderson, Westmont, N. J.,assignor to Radio Corporation of America, a corporation of DelawareApplication June 30, 1936, Serial No. 88,174

10 Claims. (Cl. 179138) This invention relates to electroacousticalapparatus of the type disclosed in United States Reissue Patent No.19,115 of Harry F. Olson and Julius Weinberger, and has for itsprincipal ob- Ject the provision of an improved arrangement of theacoustic labyrinth of the pressure.responsiv e element of such devices.

As pointed out in the aforesaid patent, a sound pickup device ormicrophone of the ribbon type may be operated partly in response to thepressure of a sound wave and partly in response to the pressure gradientof the sound wave by terminating a portion of the ribbon diaphragm in apipe or tube containing damping material. Such a microphone has theadvantage that its response is substantially uniform throughout a.

comparatively wide angle.

The tube into which the pressure responsive part of the ribbonterminates inthe construction of the above-noted patent has resulted in.increasing the bulk of the microphone and militating somewhat againstits appearance and portability. To overcome these disadvantages, it hasbeen proposed to make the pipe or tube as a labyrinth formed byassembling a plurality of block-like rectangular members within a casingsecured to the frame structure of the microphone, the blocks beinggrooved to provide communicating passages. Such a device is de- 30scribed on page 145, volume 5 of the Journal of Acoustical Society ofAmerica (Qctober, 1935) in an article by Weinberger, Olson and Massaentitled A Uni-directional ribbon microphone." The right angled bends atthe turns of this laby- 5 rinth, however, producerefiections which areunfavorable to the proper operation of the micro-' Moreover, noprovision is made to pr e-.v

phone. vent leakage of air from the labyrinthian tube,

and another disadvantage of the structure dis-1 40 closed in theforegoing article is that the coupling transformer between themicrophone and the amplifier is so located that the leads from it to theribbon are quite long, thereby introducing unnecessary resistance inwhat should be a low impedance circuit.

It is a further object of my invention, therefore, to provide animproved uni-directional microphone of the ribbon type which will befree from the foregoing disadvantages.

to Another object of my invention is to provide an improved microphoneas aforesaid in which the pipe or tube which loads the pressure actuatedsection presents no abrupt changes in direction for the passage of thewaves.

55 Still another object of my invention is to provide, in a microphoneof the type described, a labyrinthian loading tube constituted by aplurality of sections assembled in predetermined relation and betweenwhich no leakage of air will 1 take place, 1 5 5 A further object of myinvention is to provide an improved labyrinthian structure as aforesaidwhich can be readily assembled in proper relation and adjustably pressedfirmly together.

Still a further object of my invention is to 10 provide an improvedmicrophone 'of the type set forth in which the ribbon tension may bereadily adjusted to obtain suitable tension thereon. -Another object ofmy invention is to provide an improved microphone as described above inwhich the transformer is so arranged that the leads therefrom to theribbon are of minimum length.

It is also an object of my invention to provide an improved microphoneof the typeset forth 20 which is simple and compact in construction,which is comparatively light in weight and easily portable, which iseconomical of manufacture, which can be readily assembled even byunskilled workers without danger of improperassembly, and which ishighly efiicient in use.

In accordance with my present invention, I make the major portion of theaforementioned tube in which the pressure actuated portion of the ribbonterminates of a plurality of cylindrical sections arranged to provide acontinuous tubular path which is partly substantially helical and partlyspiral. The use of cylindrical sections instead of rectangular sectionspermits a. much simpler construction, and the combined helical andspiral path eliminates the right angled bends at which reflections takeplace; The cou- .pling transformer is placed in a cylindrical caseformed by several of the uppermost sections, which .lie adjacen'tthefield structure or ribbon, 40 instead of near the lowermost sections, asin the construction described above, whereby only very short leads arerequired from the transformer to the ribbon. Leakage between sections isprevented by means of resilient gaskets disposed between the cylindricalsections. These gaskets may be of rubber, for example, and may beconveniently cemented to the bottom of each section.- Proper alignmentof the sections is maintained by providing a keyslot in the periphery ofeach one and fitting each slot onto a guide rod, and a plurality of setscrews associated with a pressure plate at the bottom of the assemblymay be employed for pressing the sections firmly against each otherafter assembly.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. Howeventheinvention itself, both as to its organization and 5 method of operation,as well as additional objects and advantages thereof, will best beunderstood from the following description of one embodiment thereof,when read in connection with the accompanying drawings in which Figure 1is a perspective view of one form of Figure 7 is a detail sectional viewtaken on the line 1--1 of Fig. 5, Figure 8 is a plan view of the nextlower section of the acoustic labyrinth,

Figure 9 is a central sectional view thereof taken on the line 99 ofFig. 8,

Figure 10 is a plan view of the third lowest section of the acousticlabyrinth,

Figure 11 is a central sectional View thereof taken on the line |||l ofFig. 10,

Figure 12 is a plan view of the fourth and sixth'lowest sections of theacoustic labyrinth, Figure 13 is a central sectional view thereof takenon the line |3|3 of Fig. 12,

Figure 14 is a plan view of the fifth and seventh lowest sections of theacoustic labyrinth,

Figure 15 is a central sectional view thereof 4 taken on the line |5|5of Fig. 14, and

Figure 16 is a detailed fragmentary elevation showing the ribbontensioning means according to my invention.

Referring more particularly to the drawings,

wherein similar reference characters designate corresponding partsthroughout, there is shown, in Fig. 1, a supporting yoke I provided withan internally threaded mounting socket 2 which is suitable for mountingon a stand, the yoke I carrying a cylindrical casing member 3 which isclosed at each end by the end plates 5 and 1 threadedly receivedthereon. The upper end plate 5 supports a bracket 8 on which are mountedone or more permanent magnets 9, a clamping member serving to clamp themagnets 9 together if more than one magnet is employed.

The bracket 8 also supports a pair of pole pieces l3 in contactingrelation with the magnets 9 and in spaced relation to each other toprovide 0 an air gap therebetween in which a conducting element ismounted for vibratory movement.

The conducting element may comprise a thin, elongated, transverselycorrugated ribbon clamped at each end and also at its center to 05provide two independently actuable ribbon portions l5 and I1, theportion l5 being freely accessible to sound waves from both the frontand l the back whereby it is responsive to the pressure gradient, orvelocity, component of a sound 70 wave, and the portion l1 being coveredat its rear by the somewhat expanded end l9 of a tube or pipe 2| wherebythe portion I1 is accessible to sound waves only from the front andtherefore is responsive only to the pressure component 75 thereof. Apair of conductors 23 connected to the upper end of the ribbon portionl1 and a conductor 25 connected to the lower end of the ribbon portion|5 couple the conductive element |5|1 to a coupling transformer (notshown) which in turn connects the microphone to suit- 5 able amplifyingmeans (also not shown) through a cable 21, the conductors 23 and 25being, preferably, arranged in the manner set forth in the United Statespatent of Harry F. Olson and Barton Kreuzer, No. 1,897,732. Preferably,also, 10 the parts just described are housed within a perforatedprotecting casing (not shown) adapted to be fitted into a cup-likemember 29 on the plate 5.

The pipe or tube 2| terminates into a laby- 15 rinthian acoustic loadingtube constituted by passages formed in a plurality of cylindricalsections 3|, 33, 35, 31, 39, 4| and 43 housed within the cylindricalcasing 3. The uppermost sections 3|, 33 and 35, which are nearest to thevibratile con- 20 ducting ribbon |5-|1, are toric in shape and enclose aspace 45 within which is placed a cylindrical casing 41 of highlypermeable material for housing the aforementioned coupling transformer.By reason of the proximity of this transformer to the ribbon |5| 1, itwill be obvious that the leads23 and 25 may be made very short inlength, and therefore no unnecessary resistance is introduced into themicrophone circuit.

The passage 49 in the section 3| is generally circular in shape and hasan inlet 5| and an outlet 53. As seen in Figure '7, the inlet 5| isprovided with a smooth curve and the outlet 53 with a smooth curve 51 sothat there are no abrupt bends in the section 3|. A pin 59 serves toproperly locate the section 3| within the casing 3 with respect to thetube 2|, whereby the latter will accurately communicate with the inlet5|.

The sections 33 and 35 are quite similar to the section 3| each beingalso toric in shape and respectively having the generally circularpassages 6| and 63 therein similar to the passage 49. The passage 6| hasa smoothly curved inlet 65 with which the outlet 53 communicates, and asmoothly curved outlet 61 which communicates with the smoothly curvedinlet 69 of the passage 63, while the smoothly curved outlet 1| of thepassage 63 communicates with the passage 13 of the next succeedingsection 31. By. reason of the toric configuration of the sections 3|, 33and l 35, it will be observed that their communicating passages49--6|-63 constitute substantially a helix within the convolutions ofwhich the space or chamber 45 is provided.

Of the sections 31, 39, 4| and 43, the sections 31 and 4| are identicalwith each other, and the sections 39 and 43 are substantially identicalto oneanother, and for this reason only the sections 31 and 39 will bedescribed in detail. The section 31 is made substantially cup-shaped and1 its passage 13 has a smoothly curved inlet 15 adjacent the peripheryand a smoothly curved outlet 11 at the center of the section, thepassage 13 being in the form of an inwardly wound spiral, i. e., onestarting at the periphery and extending g5 inwardly to the center. Inthe section 39, however, of which the passage 19 is also spiral, the

' passage 19 starts at the center and travels outwardly to theperiphery, its inlet 8| and outlet 83 being also smoothly curved. Fromthe outlet 70 1| therefore, the labyrinthian passage or tube continuesthrough the inlet 15, the spiral passage 13, the outlet 11, the inlet 8|of the section 39, the spiral passage 19, and through the outlet 83.Here the labyrinth again continues through the tion l5.

spiral passages of the sections 4| and 43 in precisely the same way asthrough the sections 31 and 39, respectively, and terminates/adjacentthe periphery of the section 43, since the spiral passage in the section43 comes to a dead end instead of having an outlet. Thus, the shape ofthe labyrinth is in' part substantially. helical and in part spiral, andthroughout its entire length from.

the inlet 5! of the section 3| tothe dead end of the spiral passage inthe section 43, it constitutes a circuitous passage of graduallychanging direction and entirely free from any abrupt bends, thelabyrinth being made up wholly by the assembly of the sections 3|,, 33,35, 31,, 4| and 43 in the manner described.

In order to insure accurate assembly of these sections, theirperipheries may be marked with suitable indexing means. As shown in thedrawings, each section has a notch or key slot formed in its peripheryand a guide rod 8'! is inserted through all the slots 85 to accuratelyline up the several sections. Theoretically, the labyrinthian passageshould be of infinite length, but since this is impossible, each sectionmay have its passage filled with suitable damping material 9i, such asloosely packed, uniformly distributed hair felt, in order to-simulatethe effect of a loading tube of infinite length. This effect is furtherapproached if leakage of air between the several sections is prevented.For this purpose, there may be cemented or otherwise suitably secured tothe closed bottom of each section a rubber, leather, cork or othersimilar gasket 93, each gasket having an opening therein coinciding withthe outlet opening of the section to which it is secured and anotheropening therein coinciding with the inlet opening of the nextsucceeding, or next lowermost, section. The tops of the respectivesections are all open and their upper edges dig into the resilientgaskets when pressed together. Pressure may be applied to the severalsections by means of a plurality of set screws threaded into the bottomend plate 1 and bearing against a pressure plate 91, the pressure beingapplied after the end plate 1 has been screwed into place, as by meansof a suitable tool inserted; into the openings 99 thereof.

From the foregoing description, it will be ap parent that I haveprovided an improved acoustic labyrinth for the pressure responsiveportionv I! of the conductive ribbon. This portion of the ribbon ispreferably initially arranged as to tension during manufacture andmaintained in initially set condition; Under certain circumstances,however, it has been found desirable to change the tension of thevelocity actuated pormanner by clamping the central portion of theribbon between a pair of fixed members and its lowest end between a pairof bridge elements lfll through which a pair of set screws I03 pass,being locked thereto by the nuts ")5. The screws 103 are threadedlyreceived in the pole pieces [3 and may be adjustably fixed therein bymeans of the nuts I01.

I therefore desire that only such limitations be imposed thereon asarenecessitated by the prior art and by the spirit of the appendedclaims.

' sections.

This may be accomplished in a facile By properly manipulating the nuts a105, the desired tension may be applied to the transformer.

I claim as my invention:

1. In electroacoustical apparatus, a vibratile element, and meansassociated with at least a portion of said element for rendering saidportion responsive to the pressure of a sound wave, said meanscomprising a plurality of assembled sections each provided with acircuitous passage of gradually changing direction throughout itslength, the passages of adjacent sections communicating with each otherwhereby to provide a continuous passage.

2. The invention set forth in claim 1 characterized in that certain ofsaid sections have their passages formed adjacent their peripheries, andcertain other of said sections have their. passages extend between theirrespective peripheries and their centers.

3. The invention set forth in claim 1 characterized in that certain ofsaid sections,have their passages circularly formed adjacent theirperipha eries, and certain other of said sections have their passagesformed spirally between their respective peripheries and centers.

4. The invention set forth in claim 1 characterized in that saidsections are-each open at one end and substantially closed at the otherend, said closed ends each having an outlet opening therein terminatingthe passages in the respective sections, and characterized further bythe addition of means between adjacent sections adapted to prevent theleakage of air from between said sections.

5. The invention set forth in claim 1 characterized in that saidsections are each open at one end and substantially closed at the otherend, said closed ends each having an outlet opening therein terminatingthe passages in the respective sections, characterized further by theaddition of resilient means between adjacent sections for preventing theleakage of air from between said sections, and characterized stillfurther by the addition of means for adjustably pressing said sectionsinto firmly engaging relation.

6. The invention set forth in claim 1 characterized in that each of saidsections is provided with peripheral indexing means whereby saidsections may be assembled in proper relation to each other.

'7. The invention set forth in claim 1 characterized in that .each ofsaid sections is provided with a peripheral key slot, and characterizedfurther in that guiding means extends through all of said 0 slotswhereby to insure proper assembly of said 8. The invention set forth inclaim 1 characterized in that said section passages are individually soformed as to provide a continuous passage which is partly substantiallyhelical and partly spiral, said helical part being located nearest tosaid vibratile element and the space within the convolutions thereofproviding a chamber for housing a transformer.

9. The invention set forth in claim 1 characterized in that severaladjacent sections are toric in shape and enclose a space adapted tohouse a transformer.

10. The invention set forth in claim 1 characterized in that thoseseveral of said sections which are nearest to said vibratile elementarie toric in shapeand enclose a space adapted to house a LESLIE J.ANDERSON.

